🛠 Variateur lumineux en PWM (broches 3, 5, 6, 9, 10)

Objectives

Vary the brightness of an LED using analogWrite (PWM) and understand the specific constraint of the Nano Every: PWM is only available on pins 3, 5, 6, 9, and 10. Pin 11, which supports PWM on a classic Uno/Nano, is only a digital I/O pin on this board — a common pitfall when reusing shields.

Hardware

• 1 × Arduino Nano Every
• 1 × LED + 1 × 220 Ω resistor
• 1 × 10 kΩ potentiometer (connected to A0)
• Jumper wires, micro-USB cable

Complete Code

// Potentiometre A0 -> variation PWM sur broche 9
// Rappel: PWM possible uniquement sur 3, 5, 6, 9, 10 (pas 11 !)
const uint8_t LED_PWM = 9;
const uint8_t POT = A0;
uint32_t tPrecedente = 0;

void setup {
  pinMode(LED_PWM, OUTPUT);
  Serial.begin(9600);
}

void loop {
  if (millis - tPrecedente < 20) return;
  tPrecedente = millis;

  uint16_t brut = analogRead(POT);            // 0..1023
  uint8_t rapport = map(brut, 0, 1023, 0, 255);
  analogWrite(LED_PWM, rapport);              // 0..255
  Serial.print("rapport="); Serial.println(rapport);
}

Expected Verification

The LED gradually turns off and then increases in brightness as you turn the potentiometer. Using an oscilloscope or logic analyzer on pin 9, you will see a square wave whose duty cycle follows the input value. Test the same code on pin 11: the LED simply stays on or off — proving that PWM is not available there.

Common Errors

• Using analogWrite on pin 11 (or 4, 7, 8…): no PWM effect, the pin remains in digital on/off mode; check digitalPinHasPWM(pin) in your code.
• Forgetting the series resistor with the LED: while 5 mA per LED might seem safe, it unnecessarily stresses the chip.
• Expecting the same frequency as the classic Nano: the megaAVR core remaps the timers (configurable TCA/TCD), so PWM frequencies are not identical to the old core — this matters for motor control or audio playback.
• Value confusion: analogWrite takes values from 0-255, while analogRead returns values from 0-1023 — hence the need for map.
• "Flickering" LED at low duty cycle: this is the perceptible flicker of PWM at low frequencies; normal in educational contexts.